The present disclosure relates to generating timing signals for controlling read/write operations in rotating magnetic storage devices.
A hard disk drive (HDD) typically includes at least one disk having a magnetic medium for storing information. A surface of a disk includes radially spaced, concentric data tracks. Each data track is divided into data sectors. Embedded servo sectors forming servo wedges are written on the disk surface. The servo sectors provide information for positioning the read/write head over a track during read and write operations.
To maximize data density, data is written to the disk such that data density is substantially uniform throughout the disk. The disk is rotated at a constant angular velocity while varying the data rate from an inner diameter zone to an outer diameter zone. To vary the data rate, the data clock is synchronized to the speed of the disk relative to the position of the head.
A time base generator can be used to generate a clock signal for controlling the read and write frequency. The frequency can be changed at each servo wedge to provide an optimum bit error rate (BER) and improve average data density. This frequency change should settle within a servo gate period (e.g., approximately 160 nanoseconds). A time base generator in a HDD is typically based on a phase-locked loop (PLL) which has a settling time that is restrained by the update rate and stability inherent of the PLL (e.g., approximately 1 to 2 microseconds).